You can also just Google it. A quick search shows the tow rating with a V6 to be 5klbs. Check the tires as well, but most likely they will be ok unless they were replaced with the cheapest possible replacements.
From what I remember, all 4Runners came with a towing package, so there was no difference between models as far as tow ratings go; V8 4Runners were rated at 7klbs (give or take for 2WD and 4WD) and V6 4Runners were rated at 5klbs. You should already have the trans cooler, wiring, etc, that will set the vehicle up for its rating. There is also a sticker on the hitch that will show the rating (the vehicles with higher ratings got better hitches) so I believe that the sticker on the hitch matches the actual tow ratings in most (all) cases.
As long as you look at trailers in the 3,500lb range, you shouldn't have a problem. The 4Runner is a great platform, and it's only real drawback is the short wheelbase.
'11 G2 32BHDS